1. Field of the Invention
The present invention relates to a process for preparing a metamorphosed alkali metal titanate.
2. Description of the Prior Art
Alkali metal titanates are represented by the formula EQU Ma.sub.2 O.nTiO.sub.2.mH.sub.2 O
wherein Ma is an alkali metal, n and m are respectively an integer not more than 10, and are well known as insulating materials having excellent heat resistance and high refractive index. Recently, many attempts have been made to modify or metamorphose such alkali metal titanates, in accordance with diversified industrial needs. Thus, attempts have been with a view to lowering the insulating property of an alkali metal titanate or, in other words, making an alkali metal titanate semiconductive and further conductive, without extinction of its heat resistance and its reinforcing property for composites owing to its shape, or with a view to coloring an alkali metal titanate having in general a large refractive index and high whiteness and being difficult to apply to colored materials, into black, blue, etc.
Heretofore, there has been a well known process for making an alkali metal titanate electroconductive, for example, by heating and metamorphosing a mixture of titanium dioxide and various sodium salts under a hydrogenous atmosphere to form a hydrogenated sodium titanate. In such process, it was necessary to heat the above-mentioned mixture at a high temperature of approx. 800.degree. to 1200.degree. C. in a hydrogenous atmosphere. The heating at a high temperature in a hydrogenous atmosphere, however, is extremely dangerous. That is, the known process involved various problems to be solved for the insurance of safety, with regard to manufacturing equipments and process controls. Furthermore, hydrogenated sodium titanates obtained by said process release hydrogen and as a result lose conductivity when they are brought in contact with an oxidative atmosphere. Thus, the sodium titanates were restricted in application.
Under the circumstances, the inventors of the present invention have already proposed processes to prepare metamorphosed alkali metal titanates in the presence of a carbonous compound under a non-oxidative atmosphere (Japanese Patent Laid-open Nos. sho.58-135129 and sho.58-135130). However, it has been noted after further investigation that the carbonous compounds used in said processes and contained in the metamorphosed alkali metal titanates (1) lower the heat resistance characteristic of alkali metal titanates and (2) decrease the bulk density, and accordingly there is difficulty in mixing and dispersion of the products with other materials to obtain composites. Thus, it was necessary to separate the carbonous compounds in order to obtain metamorphosed alkali metal titanates having excellent heat resistance.
It is an object of the present invention to provide a novel process for preparing metamorphosed alkali metal titanates having excellent heat resistance and electroconductivity, which are free from disadvantages as mentioned above.